import java.util.*;
public class Main {
    public static void main(String[] args) {
        System.out.println("Hello world!");
    }

    /**
     * 合并两个有序链表
     * @param list1
     * @param list2
     * @return
     */
    public static ListNode mergeTwoLists(ListNode list1, ListNode list2) {
        if(list1==null){
            return list2;
        }
        if(list2==null){
            return list1;
        }
        if(list1.val>list2.val){
            list2.next=mergeTwoLists(list1,list2.next);
            return list2;
        }else{
            list1.next=mergeTwoLists(list1.next,list2);
            return list1;
        }
    }
}